I found Mr. Muscle declogger at the supermarket.
According to the product information, It says that Mr Muscle Kitchen & Bathroom Foamer is the powerful solution to clear slow running sinks, plugholes and pipes in your bathroom and kitchen.

So I tried it!
After 30minutes,the drainage of my bathroom turned to be fine!

“What a great product it is!” I shouted.
I would recommend this product to everyone who suffers the same problem.

P.S
I recommended this product to my friend, and he also solved his problem.